Concealed weapons detection systems are used in a wide range of situations in order to provide added security against violent crimes. In addition to the well-known use of concealed weapons detection systems in public airports, such weapons detection systems are increasingly being used in court houses, schools and other public/governmental facilities that may be subject to threats or attacks by various members of the public.
One commonly used concealed weapons detection system is the electromagnetic (EM) induction system. Essentially, an EM induction system operates by periodically broadcasting an electromagnetic pulse or series of pulses, usually in the kilohertz range. It is believed that the transmitted electromagnetic pulse induces an electrical current or currents in electrically conductive objects contained within the sensing area. The induced electrical current or currents create their own electromagnetic signals which are then detected by a suitable detector associated with the weapons detection system.
While EM induction systems of the type described above have been used for decades as concealed weapons detection systems, they are not without their problems. For example, such EM induction systems are generally sensitive to the overall size, i.e., surface area of the object, not its mass. Consequently, small, compact, but massive objects, such as a small pistol, may not produce a "signature" that is significantly larger than the signature produced by a light weight object of the same size, such as keys or pocket change. Another problem associated with EM induction systems is related to the fact that EM systems are sensitive to electrically conductive objects, regardless of whether they are magnetic or non-magnetic. That is, EM systems tend to detect non-magnetic objects, such as pocket change, just as easily as magnetic objects (e.g., weapons). Consequently, EM systems tend to be prone to false alarms. In many circumstances, such false alarms need to be resolved by scanning the suspect with a hand-held detector in order to confirm or deny the presence of a dangerous weapon.
Accordingly, a need exists for an improved weapons detection system that reduces or eliminates some of the shortcomings and problems associated with conventional, EM-induction systems. For example, such an improved weapons system should have improved sensitivity and selectivity to reduce the occurrence of "false alarms," i.e., the detection of metals and materials that are not weapons. If the improvements in sensitivity and selectivity were significant, such an improved weapons detection system could be more safely monitored from a remote location. Indeed, several such systems could be monitored from the same location. The detection system or system could also be concealed, thereby reducing the number of circumvention attempts that are typically associated with more conspicuous detector systems. Additional advantages could be realized if such a system would be reliable and relatively inexpensive to implement and operate.